Constant strain boot seal

ABSTRACT

An elastomeric seal apparatus (16) having an inner annular terminating portion (36) which is attachable to a first (12) member, an outer annular terminating portion (38) which is attachable to a second (14) member, and an annular convoluted flexible portion (40) which is disposed between the inner (36) and outer (38) terminating portions and has an inner (46) and an outer (48) margin which are respectively joined thereto. The thickness of the convoluted flexible portion (40) decreases from the relatively thicker inner margin (46) to the relatively thinner outer margin (48) in proportion to a radial distance (H) extending from the inner margin (46) to the flexible portion (40). A concentrically inner convolution (42) and a concentrically outer convolution (44) constitute the flexible portion (40) and have a relatively small (R 1 ) and a relatively large (R 2 ) radius of curvature. When the inner (36) and outer (38) terminating portions are relatively reciprocated with the first ( 12) and second (14) members about a longitudinal seal axis (16a), the tapered, convoluted structure of seal apparatus (16) exhibits extended life as a result of substantially equalizing the maximum uniform strains induced therein.

DESCRIPTION

1. Technical Field

This invention relates generally to impact apparatus for fracturingmaterial and, more particularly, to a relatively reciprocatableshank/housing configuration which facilitates sealing therebetween.

2. Background Art

Numerous apparatus are available for fracturing rock formations andother materials in mining, excavation, and earthmoving in general.Fracturing materials by blasting with explosives can be an efficienttechnique, but may, under some circumstances, present an unacceptablyhigh risk when used near population centers.

Mechanical impact apparatus such as jack hammers and/or crank drivenimpactors are known but are relatively slow and inefficient orconstitute bulky devices which are not easily manipulated into limitedaccess places.

U.S. Pat. No. 3,868,145 which issued Feb. 25, 1975, and U.S. Pat. No.3,922,017 which issued Nov. 25, 1975, both being assigned to the presentinvention's assignee, illustrate two highly efficient, compact,manipulatable material fracturing devices. Each of the devices includesa fracturing shank which is reciprocatably mounted adjacent a powersupply housing. The shank, during operation, reciprocates between afirst impact receiving position and a second, material fracturingposition where the fracturing shank is in penetrating contact with thefracturable material. In U.S. Pat. No. 3,868,145 the fracturing shankhas an impact receiving portion which protrudes into the housing and isintermittently impacted by a rotatable eccentric to provide suchreciprocating motion. In U.S. Pat. No. 3,922,017, an intermediate hammermember extends into the energy supply housing and is used to transferenergy generated and stored within that housing to an impact receivingportion of the shank which is external to the housing. Such intermediatehammer member extends into and is, likewise, reciprocably mountedrelative to the housing.

In each of the aforementioned apparatus the reciprocatable member whichextends into the energy supply housing must be sealed to the housing toretain lubricant within the housing and prevent foreign particleintrusion into the housing. Moreover, seal apparatus providing suchsealing must be attached to the reciprocatable member (shank orintermediate hammer) to avoid transporting foreign debris into thehousing on the surface of the reciprocatable member when it moves fromits second to its first position. Sliding seals such as are commonlyused in hydraulic cylinder applications and are illustrated in U.S. Pat.No. 4,121,845 which issued Oct. 24, 1978, U.S. Pat. No. 2,188,106 whichissued Jan. 23, 1940, U.S. Pat. No. 2,881,015 which issued Apr. 7, 1959,U.S. Pat. No. 4,021,049 which issued May 3, 1977, U.S. Pat. No.3,403,932 which issued Oct. 1, 1968, U.S. Pat. No. 3,285,632 whichissued Nov. 15, 1966, U.S. Pat. No. 3,317,215 which issued May 2, 1967,U.S. Pat. No. 4,003,666 which issued Jan. 18, 1977, and U.S. Pat. No.4,003,667 which issued Jan. 18, 1977, are, thus, not suitable for use insuch material fracturing apparatus since they can permit transportationof such foreign debris into the housing.

A type of boot seal, illustrated in U.S. Pat. Nos. 3,868,145 and3,922,017, is attached to both the housing and the reciprocatable memberwhich extends into the housing. While the impacting apparatus describedin the immediately herebefore U.S. Patents have, in general, fracturedmaterial in an efficient manner, the life of the boot seals has beenerratic. A short boot seal life is highly undesirable since repair orreplacement of such boot seal can be a time consuming process which mustoften be performed under field conditions. Moreover, during such repair,the impact fracturing apparatus utilizing the boot seal must be shutdown.

DISCLOSURE OF THE INVENTION

In one aspect of the present invention a seal apparatus is provided forsealing between relatively reciprocatable members and includes anannular flexible portion having an inner margin, an outer margin, and aplurality of concentrically arranged, interconnected convolutions whichhave a thickness which is tapered from the inner margin to the outermargin.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription of a preferred embodiment taken in connection with theaccompanying drawings in which:

FIG. 1 is a partial transverse sectional view of a material fracturingapparatus in which the invention is incorporated;

FIG. 2 is an enlarged view of a portion of FIG. 1;

FIG. 3a is a front elevational view of a portion of a seal used in theapparatus illustrated in FIGS. 1 and 2;

FIG. 3b is a transverse sectional view of the seal illustrated in FIG.3a;

FIG. 4 is a front elevational view of a seal retaining ring used tosecure the seal to a housing illustrated in FIGS. 1 and 2; and

FIG. 5 is a rear elevational view of a portion of a shank illustrated inFIGS. 1 and 2.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to the drawings in detail, FIG. 1 illustrates an impactfracturing apparatus 10 having an arcuately reciprocatable shank member12, a housing 14 having an interior 15 into which the shank 12 isarcuately reciprocatable, and an annular seal member 16 connected to thereciprocatable shank 12 and the housing 14 and having a longitudinalseal axis 16a. The shank 12 is reciprocatable between a first, extremeimpact receiving position (illustrated in full) and a second, extremematerial fracturing position (illustrated in phantom). Arcuatereciprocation of the shank 12 to the right (as viewed in FIG. 1) beyondits first, extreme impact receiving position is precluded by a stoppingmember 18 which abuts the shank 12 when it reaches its first extremeposition. Likewise, a stopping member 20, which is disposed on theopposite side of the shank 12 and is preferably attached to a stationarycasing member 21 (attachment not shown), abuts the shank 12 when itreaches the second, extreme material fracturing position. A pin 22pivotally joins the shank 12 to the casing member 21 which also supportsthe housing 14 to constrain the reciprocation of the shank 12 along anarcuate path about a pivot axis 24.

The shank 12 includes a sealing portion 26, an impact receiving portion28, and a fracturing tip 29. As better illustrated in FIG. 2, theshank's sealing portion 26 has a cylindrical sealing surface 26a and alongitudinal axis 26b about which the cylindrical sealing surface 26a isdisposed. The impact receiving portion 28 has a longitudinal axis 28band an impact receiving surface 28a which is engageable at intermittenttimes with a rotatable eccentric impacting member 30. A shank guidestructure 31 includes two shank guides 32 (the one nearer the viewerhaving been removed to provide better visibility of the impact receivingportion 28) which are fixedly attached to the housing interior 15 andtogether transversely define an opening within which the impactreceiving portion 28 is receivable. The shank guides 32 are arranged inclosely spaced, transverse relation with the impact receiving portion 28so as to direct the impact receiving surface 28a into an optimum impactreceiving relationship with the impact member 30 and to resisttransversely directed forces exerted on the shank 12 by the impactingmember 30 and by the fracturable material. The shank guides 32 have anaxial length 32a which is greater than the distance separating theextreme reciprocation positions of the shank's impact receiving surface28a as illustrated in FIG. 1. The mechanism for intermittently engagingthe impacting member 30 with the impact receiving surface 28a is betterdescribed in U.S. Pat. No. 3,868,145 which issued Feb. 15, 1975, and isassigned to the present invention's assignee. The sealing surface'slongitudinal axis 26b is perpendicular to a line 33 which extendsradially from the pivot axis 24. As a result, the longitudinal axis 26bremains perpendicular to the radial line 33 for all positions assumableby the shank 12 along its arcuate reciprocation path. The sealingsurface's longitudinal axis 26b is inclined relative to the impactreceiving portion's longitudinal axis 28b by an angle of approximately10° by example.

The annular elastomeric seal 16 (best illustrated in FIGS. 3A and 3B)has a relatively rigid inner terminating portion 36 and a relativelyrigid outer terminating portion 38 which are respectively fixedlyattached to the sealing surface 26a and the housing 14 so as to preventdebris intrusion into the housing's interior 15 and to prevent lubricantleakage out of the housing's interior 15. When the shank 12 assumes theposition illustrated in FIG. 2 which is intermediate its extremereciprocation positions, the seal apparatus 16 is unstrainedsymmetrically disposed about the longitudinal seal axis 16a and thesealing surface's longitudinal axis 26b coincides with the seal'slongitudinal axis 16a. The seal 16 includes an annular flexible portion40 which is disposed between and joined to the relatively rigidterminating portions 36 and 38. A plurality (in this case two) ofconcentrically arranged interconnected convolutions 42 and 44 togetherconstitute the flexible seal portion 40. The convolutions 42 and 44 havea convoluted centersurface 16b which appears as a centerline in FIG. 3B.It is to be understood that the centersurface 16b is the locus of pointstraced by the centerline illustrated in FIG. 3 as it is rotated aboutthe longitudinal axis 16a. It is to be further understood that thecentersurface 16b is an imaginary surface which is introduced forreference purposes only.

The convolutions 42 and 44 respectively include an inner and an outermargin 46 and 48 which bound the flexible portion 40, interface with theinner and outer terminating portions 36 and 38 respectively, and haveexemplary thicknesses perpendicular to the centersurface 16b of 4 mm and3 mm, respectively. The inner margin 46 constitutes the effective inneredge of the flexible portion 40 and is disposed along the radial line33. The inner convolution 42 has a smaller radius of curvature R₁ of17.77 mm by example as measured from an axis of curvature O₁ to thecentersurface 16b than does the outer convolution 44 whose radius ofcurvature R₂ of 23.69 mm by example is measured from an axis ofcurvature O₂ to the centersurface 16b. The axes of curvature O₁ and O₂(illustrated in FIG. 3B) are separated, or offset, by a distance whichis designated generally by the reference letter O and, by example,equals 16.0 mm.

It is to be understood that the previously mentioned sizes anddimensions for the seal 16 correspond to a seal which utilizes anelastomer material commonly known in the trade as Hytrel. A suitablealternative seal material constitutes fabric reinforced neoprene rubberwhich varies in exemplary thickness from 7 mm at the inner margin 46 to5 mm at the outer margin 48. The offset O of the radii of curvature byexample equals 10.0 mm while the radii of curvature for the inner andouter convolutions 42 and 44, respectively, constitute 16.78 mm and22.37 mm for such fabric reinforced neoprene seal material.

The inner and outer margins 46 and 48 respectively interface with andare connected to the inner and outer terminating portions 36 and 38. Thethickness of seal 16 perpendicular to the centersurface 16b varies fromthe inner margin 46 to its outer margin 48 with decreases from the innermargin's thickness being proportional to the radial distance H(illustrated in FIG. 3B) separating the centersurface 16b at the innermargin 46 from the centersurface 16b at the seal location in question.The seal's terminating portions 36 and 38 have thicker cross sections(as measured perpendicularly to the centersurface) than the flexibleportion 40 since the terminating portions 36 and 38 are actually joinedto the relatively reciprocatable shank 12 and housing 14. The flexibleseal portion 40 has isolation faces 50 and 52 which are equidistant fromthe convoluted centersurface 16b and are respectively exposed to theenvironment surrounding the impact apparatus 10 and that existing in thehousing's interior 15.

The seal 16 further includes an annular connection member 54 of U-shapedcross section which is disposed about and vulcanized bonded to the innerterminating portion 36. The U-shaped connection member 54 is open alongthe axial end adjacent the inner margin 46 and is closed on the oppositeaxial end. The connection member 54 has a radially inwardly facingsurface 56 which is threadably engageable with the sealing surface 26a.A plurality (two in the illustrated case) of openings 57 in theconnecting member 54 are provided to receive a tightening tool used torelatively rotate and threadably engage the seal 16 and the sealingsurface 26a with a predetermined torque. A cylindrical locking extension58 protrudes from the connection member 54 and is deformable into aplurality of restraining slots 59 (best illustrated in FIG. 2) formed inthe shank 12 to prevent relative rotation of the connection member 54and the sealing surface 26a in a threadably disengaging direction.

A retainer ring 60, illustrated in FIGS. 1, 2, and 4, is engageable withthe seal's outer terminating portion 38 and is securable to the housing14 by a plurality of threaded screw bolts 62. The retaining ring 60 isannular relative to the longitudinal seal axis 16a except in thevicinity of a vertical centerline therethrough where the retainingring's radial thickness is reduced to permit disposition thereof betweenthe seal's outer terminating portion 38 and the casing member 21. Theretaining ring 60 and the outer terminating portion 38 are engageablealong cooperatively ramped interfacing surfaces 38a and 60a which arerespectively disposed thereon. Tightening the screw bolts 62 displacesthe retaining ring 60 relative to the outer terminating portion 38,increases the interference therebetween as a result of the cooperativeinclination of the ramped surfaces 38a and 60a, compresses the seal'souter terminating portion 38. Optimum sealing of the seal's outerterminating portion 38 with the housing 14 and the retaining ring 60obtains when the retaining ring 60 engages the housing 14. A securingbead 38b of the terminating portion 38 extends radially inwardly and isreceivable in a circular notch 14a formed in the housing 14.

An enlarged view of the impact receiving portion 28 is illustrated inFIG. 5 as viewed from a vantage point A as indicated in FIG. 1. Theimpact receiving portion 28 has an outer periphery 28c which constitutesa four-sided figure whose corners have been rounded. The longestprotrusion of the outer periphery 28c from the impact receivingportion's longitudinal axis 28b is the radius 28d which is smaller thanthe radius separating the sealing surface 26a from the sealinglongitudinal axis 26b. Such size differential enables axial displacementof the seal 16 over the impact receiving portion's outer periphery 28c.

Industrial Applicability

With the fracturing apparatus 10 assembled as previously described,highly effective sealing is provided between the arcuatelyreciprocatable shank 12 and the housing 14 by the seal 16 which isfixedly joined to both. When the impact receiving portion 28 of theshank is in its first extreme position (furthest intrusion into thehousing's interior 15 between the shank guides 32), the sealingsurface's longitudinal axis 26b is skewed relative to the seal'slongitudinal axis 16a. A coincident relationship between the seal'slongitudinal axis 16a and the sealing surface's longitudinal 26b axisobtains when the shank 12 occupies the position illustrated in FIG. 2.Arcuate reciprocation of the shank 12 in either direction from theposition illustrated in FIG. 2 results in a pivoting of the sealingsurface's longitudinal axis 26b relative to the seal's longitudinal axis16a. Such relative pivoting of the longitudinal axes 16a and 26bnecessarily occurs since the sealing surface 26a is constrained to pivotabout the pivot axis 24 while the seal's longitudinal axis 16a remainsfixed since it is defined by the configuration of seal 16 when it isunstrained. The seal's longitudinal axis 16a thus occupies a stationaryposition relative to the housing 14. The center of the shank's impactreceiving surface 28a is displaceable between the extreme reciprocationpositions illustrated in FIG. 1 through a distance of approximately 70mm by example. When the shank 12 occupies the second or extreme materialfracturing position, the maximum strain on the seal 16 is approximately9.6% which is significantly lower than the strain levels encountered inprevious seals used in similar material fracturing apparatus.

Canting the shank's sealing portion 26 relative to the shank's impactreceiving portion 28, providing a concentric relationship between theseal 16 and the sealing portion 26 for one position of the shank 12, andarranging the seal's inner margin 46 along the radial line 33 as well asutilizing the seal geometry previously described results in greatlyreduced strain levels in the seal 16 which are substantially equal atthe points of maximum strain. Oscillation of the shank about the pivotaxis 24 is necessary to provide the desired reciprocating motionthereto. At the seal's inner terminating portion 36, this oscillationproduces an arcuate motion which may be resolved into two perpendicularcomponents of displacement: an axial displacement component parallel tothe longitudinal axis 16a of the unstrained seal 16 and a radialdisplacement component perpendicular to the unstrained seal axis 16a.Such radial displacement can be visualized by noting that the top (asviewed in FIG. 1) of the seal's terminating portion 36 will slightlyapproach the top of the seal's terminating portion 38 simultaneouslywith the bottom of the seal's terminating portion 36 moving away fromthe bottom of the seal's terminating portion 38. Seal strain produced bythe combined axial and radial displacements is greater than thatproduced by the axial displacement alone, primarily because the radialdisplacement deforms the seal into an unsymmetrical configurationrelative to the longitudinal axis 16a of the unstrained seal. It wasfound that the additional strain resulting from such radial deflectionof the seal 16 could be minimized by: (1) canting the seal 16 and thesealing portion 26 to provide perpendicularly between the radial line 33and the longitudinal axis 26b; and (2) arranging the seal's inner margin46 (located where the seal 16 becomes rigid or is effectively attachedto the shank 12) along the radial line 33. Cooperatively canting thelongitudinal axes 26b and 16a to provide coincidence thereof when theshank configuration of FIG. 2 occurs reduces the strain in the seal 16during arcuate reciprocation of the shank 12 while the seal's taperedwall thickness and convoluted shape equalizes the maximum strainsinduced therein. The geometrical features of seal 16 which areresponsible for providing such substantially equalized maximum strainsare the tapered thickness which is a function of the radial distance H,the convolutions' different radii of curvature R₁ and R₂, and the offsetdistance O between the axes of curvature.

The seal 16 may be removed from the material fracturing impact apparatus10 by extracting the screw bolts 62, removing the retaining ring 60,disengaging the deformed areas of the locking extension 58 from thelocking slots 59, and rotating the seal 16 and integral connectionmember 54 to threadably disengage them from the sealing surface 26a.After moving the stopping member 20 to an unobstructing position, theshank 12 is arcuately displaced to a convenient position where theimpact receiving portion 28 is disengaged from the shank guides 32 andis resident outside the housing's interior 15. The seal 16 is thenaxially displaced along the outer periphery 28c of the impact receivingmember 28 until it passes the impact receiving surface 28a and can beremoved to a remote location. Assembly of the seal 16 is accomplished inthe opposite order as just described: the stopping member 20 is moved toan unobstructing position; the shank 12 is arcuately displaced to aposition where the impact receiving portion 28 is exterior to thehousing 14; the seal 16 is slidingly displaced over the impact receivingportion's outer periphery 28c; the seal 16 and integral connectionmember 54 are rotated relative to the threaded sealing surface 26a untilthey are threadably engaged to a suitable tightness; areas of thelocking extension 58 which are aligned with the restraining slots 59 aredeformed thereinto; the terminating portion 38 of seal 16 is engagedwith the housing 14 such that the restraining bead 38b is inserted inthe notch 14a to secure the seal 16 in place and facilitate assembly ofthe retaining ring 60; the retaining ring 60 is disposed on the oppositeside of the seal's terminating portion 38 from the housing 14; and thescrew bolts 62 are inserted through the retaining ring 60 and torquedinto the housing 14 to provide the desired sealing between the seal'sterminating portion 38 and the housing 14.

During shank reciprocation, the cross section of the flexible sealportion 40 flexes between an "S-shape" and a nearly straight line asillustrated in FIG. 1. The respective orientation of the convolutions 42and 44 toward and away from the housing 14 cause fracturable materialand other debris exposed to the isolation face 50 to be expelledtherefrom during seal flexure and thus avoid potentially debilitating,seal immobilizing debris accumulation on the isolation face 50. TheU-shaped cross section of the connection member 54 shields thevulcanized bond from direct impingement by fracturable material duringshank reciprocation and maximizes the bonding area between the sealmaterial (preferably Hytrel) and the connection member 54 (preferablycarbon steel) for the purpose of reducing the stress (and thusincreasing the life) imposed thereon during shank reciprocation.

While the seal 16 has been illustrated as providing sealing between anarcuately reciprocatable shank 12 and a stationary housing 14, it is tobe understood that the seal 16 may be used with equal facility with thepurely translatably reciprocatable intermediate hammer member describedin U.S. Pat. No. 3,922,017 which issued Nov. 25, 1975.

It will now be apparent that a material fracturing impact apparatus 10and associated seal apparatus 16 have been provided in which thefollowing obtain: excellent sealing, exceptionally long seal life, andhigh reliability. Such attributes are necessary for practical operationof the impact apparatus 10 and seal apparatus 16 in the hostileenvironments to which they are customarily subjected.

We claim:
 1. A seal apparatus (16) for sealing between a first (12) anda second (14) relatively displaceable member, said seal apparatus (16)comprising:an annular, rigid inner terminating portion (36), an annular,rigid outer terminating portion (38), an annular flexible portion (40)having an inner margin (46), an outer margin (48), a longitudinal axis(16a), and a plurality of concentrically arranged, interconnectedconvolutions (42,44), the thickness of said convolutions (42,44)perpendicular to a convoluted centersurface (16b) therethrough decreasesfrom said inner margin (46) to said outer margin (48) in proportion to aradial separation distance (H) between the centersurface (16b) at saidinner margin (46) and the centersurface (16b) along said convolutions(42,44), said inner (36) and outer (38) terminating portions beingrespectively joined to said inner (46) and outer (48) margins and beingrespectively fixedly attachable to the first (12) and the second (14)members so as to move therewith.
 2. The seal apparatus (16) of claim 1wherein said terminating portions (36,38) have a greater thickness thandoes said flexible portion (40).
 3. The seal apparatus (16) of claim 2further comprising:a connection member (54) disposed about and bonded tosaid first terminating portion (36), said connection member (54) havinga radially inwardly facing surface (56) which is threadably engageablewith the first displaceable member (12).
 4. The seal apparatus (16) ofclaim 3 further comprising:means (58) for resisting thread disengagementrotation about said longitudinal axis (26b) between said connectionmember (54) and the first displaceable member (12).
 5. The sealapparatus (16) of claim 4, said rotation resisting means (58)comprising:a locking projection (58) having a first end joined to saidconnection member (54) and a second end extending from said connectionmember (54), said second end being deformable into slots (59) formed inthe first displaceable member (12).
 6. The seal apparatus (16) of claim1 wherein said inner convolution (42) has a radius of curvature (R₁) andsaid outer convolution (44) has a greater radius of curvature (R₂). 7.The seal apparatus (16) of claim 6 wherein said smaller radius ofcurvature (R₁) extends from a first axis of curvature (O₁) and saidgreater radius of curvature (R₂) extends from a second axis of curvature(O₂), said axes of curvature (O₁,O₂) being axially offset apredetermined distance (O).
 8. The seal apparatus (16) of claim 1wherein said outer terminating portion (38) has a ramped surface (38a)which is arranged at a predetermined angle to said longitudinal axis(16a) and a securing bead (38b) which protrudes radially inwardly tofacilitate assembly thereof with the second (14) member.